Apparatus and method for coupling the spatial light to the optical fiber light for achieving the stability of an optical axis without a position detector

ABSTRACT

An apparatus and method herein efficiently couple spatial light to optical fiber light for achieving stability of an optical axis without a position sensor. The basic concept of the method includes: first, obtaining, according to a theoretical coupling efficiency model, a model parameter by means of fitting calculation; second, using a four-point tracking algorithm to calculate an optical fiber nutation trajectory according to the optical fiber nutation principle; and finally, using the nutation trajectory to calculate the position deviation of a central point. The optical axis is ensured to be stable by correcting the position deviation, and the high coupling efficiency remains. The method is used for the stability of the optical axis in a space coherent laser communication DPSK link. The high efficiency coupling is a key technology of long-distance, high bit rate transmission in space laser communication, and is significant in the development of inter-satellite optical communications.

TECHNICAL FIELD

The invention relates to a method of efficiently coupling spatial lightto optical fiber light without a position detector for obtaining astable optical axis, which can realize coupling the spatial light tooptical fiber light with function of automatic tracking always remaininghigh coupling efficiency, which is a key technology for high code rate,miniaturization, light weight and low power consumption withinlong-distance spatial coherent laser communication.

BACKGROUND

The free spatial laser with laser beam as the information carrier hasthe advantage of high communication frequency, good spatial and temporalcoherence, and narrow emission beam, which is an effective means tosolve the bottleneck of microwave communication, build a space-basedbroadband network, and realize global high-speed, real-timecommunication, which has great potential for civilian and militaryapplication.

Space coherent laser communication is the only technical means toachieve data transmission in the rate above G bit/s in free spacelong-distance communication. Coherent laser communication based onself-heterodyne and heterodyne detection methods has high detectionsensitivity, and is a key system to achieve high code rate,miniaturization, light weight and low power consumption long-distancelaser communication terminal. For coherent laser communication, theself-heterodyne detection method needs to couple the space laser into asingle-mode fiber. Therefore, how to make spatial laser and single-modefiber couple, and make the coupling space laser to space laser couplingwith always remaining high coupling efficiency is a key technology ofhigh code rate, miniaturization, light weight and low powerlong-distance s pace coherent laser communication.

In a space coherent laser communication DPSK link, the method is usedfor stability of the optical axis of space laser and optical fiber lightwithout a position detector, which has effectively improved the couplingefficiency of space lasers, and is a new exploration of high code ratespace laser coherent communication technology, which is of greatsignificance to the development of my country's satellite-to-groundcommunication terminal. Existing solutions refer to literature (1),Morio Toyoshima “Maximum fiber coupling efficiency and optimum beam sizein the presence of random angular jitter for free space laser systemsand their applications,” J. Opt. Soc. Am. A, 2006, 23(9), (2) GaoJianqiu, Sun Jianfeng, Li Jiawei, Zhu Ren, Hou Peipei, Chen Weibiao,Coupling method of spatial light to single-mode fiber based on lasernutation. China Laser, 2016, 43 (8)

SUMMARY OF INVENTION

The purpose of the present invention is to provide a device and methodof efficiently coupling spatial light to optical fiber light without aposition detector for obtaining a stable optical axis, which can realizethe automatic tracking function of a system. The basic idea is asfollows: firstly, through the mode field matching, the couplingefficiency model parameters are calculated by fitting. Secondly,according to the principle of fiber nutation, a four-point trackingalgorithm is used to calculate the fiber nutation trajectory. Andfinally, the nutation trajectory is used to calculate the positiondeviation of the center point, and the position deviation is correctedto ensure the stability of the optical axis, and a high couplingefficiency. The technical solution of the present invention is asfollows:

a method of coupling spatial light to optical fiber light without aposition detector for obtaining a stable optical axis, which is appliedto a device comprising an optical fiber coupler and a two-dimensionalfast scanning galvanometer, wherein the method comprises at least thefollowing steps:

Step S002: the optical fiber coupler is nutated under action of anamplified orthogonal sine signal, and the two-dimensional fast scanninggalvanometer is deflected to two preset positions in x-direction andy-direction under constant voltage, and an output coupling optical powerof each position is collected respectively, and x-axis and y-axistrajectories on a nutation circumference are obtained according to theoptical power;

Step S003: the optical fiber coupler is nutated under the action of theamplified orthogonal sine signal, an optical power signal is collectedevery preset nutation period, and a position error signal is obtainedaccording to the collected optical power signal and its correspondingcoordinate value; and

Step S004: an optical path is adjusted according to the position errorsignal, thereby obtaining the stable optical axis.

Preferably, before the step S002, the method further comprises:

Step S001: coupling model parameters are obtained;

the step S001 comprises at least the following steps:

S001 a: the two-dimensional fast scanning galvanometer keeps still inthe y-direction, and performs a triangular wave scan in the x-direction,then the optical power signal of the optical fiber coupler is collected;the two-dimensional fast scanning galvanometer keeps still in thex-direction, and performs a triangle wave scan in the y-direction tocollect the optical power signal of the optical fiber coupler;

S001 b: substituting the optical power signal collected twice in S001 aand the position signal of the two-dimensional fast scanninggalvanometer corresponding to each signal point into an equation tocalculate coupling model parameters.

Preferably, the following steps are included in the method after stepS001 and before step S002:

S002 a: a signal transmitting module is controlled to transmit twoorthogonal sine signals;

S002 b: a drive signal control board divides an input signal into fouramplified sine signals which are orthogonal for each group of two sinesignals;

S002 c: the drive signal control board loads the signals onto theoptical fiber coupler via electric wires, and the optical fiber coupleris nutated under action of the amplified orthogonal sine signals.

Preferably, the step S003 comprises at least one of the following steps:

S003 a: an input signal board is controlled to transmit two orthogonalsine signals;

S003 b: a signal drive board divides an input signal into fourorthogonal amplified sine signals which are orthogonal for each group oftwo sine signals;

S003 c: the signal drive board loads signals onto the optical fibercoupler via electric wires, and the optical fiber coupler is nutatedunder action of the amplified orthogonal sine signals;

S003 d: an optical power signal is collected every a quarter of nutationperiod;

S003 e: substituting the collected optical power signal and itscorresponding coordinate value into an equation to obtain a positionerror signal.

Preferably, the amplitude of the sine signal emitted by a drive signalgenerator in step S002 a is in a range of 1V-2.5V, and a frequency is ina range of 1 kHz-5 kHz.

Preferably, the voltage amplifier in step S002 c amplifies a voltageinto 100V-200V.

Preferably, a calculated x-axis trajectory is:

${x = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \omega_{0}^{2}}} + x_{1}^{2} - x_{2}^{2}} \right\rbrack}{2 \cdot \left( {x_{1} - x_{2}} \right)}};$

And a y-axis trajectory is:

${y = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \omega_{0}^{2}}} + y_{1}^{2} - y_{2}^{2}} \right\rbrack}{2 \cdot \left( {y_{1} - y_{2}} \right)}};$

Wherein, x₁, x₂ are x coordinates of the two preset positions in thex-direction, y₁, y₂ are the y coordinates of two preset positions in they-direction, ω₀ is a coupling model parameter, P_(outx1) is an outputoptical power corresponding to the position x₁, P_(outx2) is an outputoptical power corresponding to the position x₂, P_(outy1) is an outputoptical power corresponding to the position y₁, and P_(outy2) is anoutput optical power corresponding to the position y₂.

Preferably, error positions are:

${\Delta x} = {\ln{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Rx}_{1}}}}$${\Delta y} = {\ln{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Ry}_{1}}}}$

Wherein, Rx₁ is the x coordinate on the x-direction trajectory, Ry₁ isthe coordinate on the y-direction trajectory, Wo is the coupling modelparameter, P_(outx1) is an output optical power corresponding to theposition R_(x1), P_(out)x₂ is an output optical power corresponding tothe position Rx₂, P_(outy1) is an output optical power corresponding tothe position Ry₁, and P_(outy2) is an output optical power correspondingto the position Rye.

Preferably, before step S003 or step S002, the method further comprises:

Step S000: a time delay of the two-dimensional fast scanninggalvanometer is calibrated; specifically, Step S000 comprises thefollowing steps:

Step S000 a: a sine signal K=sin(θ₁) in the X and Y directions of a faststeering mirror is loaded respectively;

Step S000 b: when the optical fiber is not nutating, a sine opticalpower G=sin(θ₂) output by an optical fiber nutator is calculated due tothe scanning of the fast steering mirror.

Step S000 c: by calculating a phase difference between K and G

A=θ ₁−θ₂

A delay time of the fast steering mirror can be obtained.

The present invention also provides a device of coupling spatial lightto optical fiber light without a position detector for obtaining astable optical axis, which is configured to perform the above method ofcoupling spatial light to optical fiber light without a positiondetector for obtaining a stable optical axis.

The present invention also provides a device of coupling spatial lightto optical fiber light without a position detector for obtaining astable optical axis, which comprises a laser (01), a beam collimator(02), a two-dimensional fast scanning galvanometer (03), a converginglens group (04), an optical fiber coupler (05), a drive signal controlboard (06), a signal transmitting module (07), a bridge (08), a detector(09), and a data acquisition board (10).

The laser (01) is connected to a port of the beam collimator (02)through an optical fiber. The emergent light of the beam collimator (02)is incident on the two-dimensional fast scanning galvanometer (03) at anangle of 45 degrees. The light beam reflected by the two-dimensionalfast scanning galvanometer (03) converges to an optical center of theconverging lens group in parallel and is incident into the converginglens group (04). The focal point of an emergent light beam of theconverging lens group (04) is incident on an end of the optical fibercoupler (05). The signal transmitted by the signal transmitting module(07) is transferred to the drive signal control board (06) throughcoaxial cables. The drive signal control board (06) loads the signalonto the optical fiber coupler (05) via electric wires. The opticalpower coupled by the optical fiber coupler (05) enters the bridge (08)via the optical fiber. An optical signal of the bridge (08) enters thedetector (09) via the optical fiber. An electrical signal of thedetector (09) enters the data acquisition board (10) via coaxial wires.

Preferably, the optical fiber coupler (05) comprises an optical fiber(11) and a piezoelectric ceramic tube (12).

Preferably, the optical fiber (11) passes through the piezoelectricceramic tube (12) and is fixed with the piezoelectric ceramic tube (12).

Preferably, the piezoelectric ceramic tube (12) includes four electroderegions (13), and electric wires (14) are welded on each of the fourelectrode regions (13).

Preferably, the signal transmitting module (07) is a signal generator.

Preferably, the drive signal control board (06) is a voltage amplifier.

The present invention also provides an optical fiber coupler whichcomprises an optical fiber, a piezoelectric ceramic tube, a couplingbase, and a electric wire;

the optical fiber is structured as a capillary with a ferrule;

the outside of the piezoelectric ceramic tube is divided into severalstrip electrode regions, which are insulated from each other;

the coupling base has holes;

the optical fiber is embedded in the piezoelectric ceramic tube, abottom end of the piezoelectric ceramic tube is fixed to the couplingbase, one electric wire extends from each electrode region of thepiezoelectric ceramic tube close to the base portion, and the other endof the electric wire passes through the hole on the base.

Preferably, an end of one end of the optical fiber has an end capcoating with high permeability film;

Preferably, the number of strip electrode regions outside thepiezoelectric ceramic tube is four;

Specifically, the above equation and its derivation process are asfollows:

1) The Coupling Model Parameters Solving: Based on Optical FiberCoupling Efficiency Model

$\begin{matrix}{P_{out} = {P_{in} \cdot B \cdot e^{{- 2} \cdot \frac{{({x - {\Delta x}})}^{2} + {({y - {\Delta y}})}^{2}}{\omega_{0}^{2}}}}} & (1)\end{matrix}$

When the light spot position is (x, y₁₁), (x, y₂₂), (x, y₃₃), (x, y₄₄),the optical fiber coupling model equation can be written as:

$\begin{matrix}{{\ln\frac{P_{{outy}_{11}}}{P_{{iny}_{11}} \cdot B}} = {{- 2} \cdot \frac{\left( {x - {\Delta x}} \right)^{2} + \left( {y_{11} - {\Delta y}} \right)^{2}}{\omega_{0}^{2}}}} & (2) \\{{\ln\frac{P_{{outy}_{22}}}{P_{{iny}_{22}} \cdot B}} = {{- 2} \cdot \frac{\left( {x - {\Delta x}} \right)^{2} + \left( {y_{22} - {\Delta y}} \right)^{2}}{\omega_{0}^{2}}}} & (3) \\{{\ln\frac{P_{{outy}_{33}}}{P_{{iny}_{33}} \cdot B}} = {{- 2} \cdot \frac{\left( {x - {\Delta x}} \right)^{2} + \left( {y_{33} - {\Delta y}} \right)^{2}}{\omega_{0}^{2}}}} & (4) \\{{\ln\frac{P_{{outy}_{44}}}{P_{{iny}_{44}} \cdot B}} = {{- 2} \cdot \frac{\left( {x - {\Delta x}} \right)^{2} + \left( {y_{44} - {\Delta y}} \right)^{2}}{\omega_{0}^{2}}}} & (5)\end{matrix}$

By equation (2) subtracting equation (3), and equation (4) subtractingequation (5) Model can be obtained by:

$\begin{matrix}{{\ln\frac{P_{{outy}_{11}}}{P_{{iny}_{22}} \cdot B}} = {{- 2} \cdot \frac{y_{22}^{2} - y_{11}^{2} + {{2 \cdot \left( {y_{11} - y_{22}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}} & (6) \\{{\ln\frac{P_{{outy}_{33}}}{P_{{iny}_{44}}}} = {{- 2} \cdot \frac{y_{44}^{2} - y_{33}^{2} + {{2 \cdot \left( {y_{33} - y_{44}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}} & (7)\end{matrix}$

Then, by simultaneous equation (6) and equation (7)

${\ln{\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}} \cdot \left\lbrack {y_{44}^{2} - y_{33}^{2} + {{2 \cdot \left( {y_{33} - y_{44}} \right) \cdot \Delta}\; y}} \right\rbrack}} = {\ln{\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}} \cdot \left\lbrack {y_{22}^{2} - y_{11}^{2} + {{2 \cdot \left( {y_{11} - y_{22}} \right) \cdot \Delta}\; y}} \right\rbrack}}$

It can be obtained by

$\begin{matrix}{{{\Delta y} = \frac{{\ln{\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}} \cdot \left( {y_{44}^{2} - y_{33}^{2}} \right)}} - {\ln{\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}} \cdot \left( {y_{22}^{2} - y_{11}^{2}} \right)}}}{{\ln{\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}} \cdot 2 \cdot \left( {y_{11} - y_{22}} \right)}} - {\ln{\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}} \cdot 2 \cdot \left( {y_{33} - y_{44}} \right)}}}}{{Due}\mspace{14mu}{to}}} & (8) \\{\omega_{0}^{2} = {2 \cdot \frac{y_{22}^{2} - y_{11}^{2} + {{2 \cdot \left( {y_{11} - y_{22}} \right) \cdot \Delta}\; y}}{\ln\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}}}}} & (9)\end{matrix}$

By substituting equation (8) into equation (9), and the coupling modelparameters can be obtained.

2) Trajectory Solving

the x-axis of the incident light spot is controlled with the use of faststeering mirror to position at two independent positions (x₁, y₀) and(x₂, y₀), and the output optical power values under the two states arerecorded respectively by

$\begin{matrix}{P_{{outx}_{1}} = {P_{in} \cdot B \cdot e^{{- 2} \cdot \frac{{({x - x_{1}})}^{2} + {({y - y_{0}})}^{2}}{\omega_{0}^{2}}}}} & (10) \\{P_{{outx}_{2}} = {P_{in} \cdot B \cdot e^{{- 2} \cdot \frac{{({x - x_{1}})}^{2} + {({y - y_{0}})}^{2}}{\omega_{0}^{2}}}}} & (11)\end{matrix}$

Taking the logarithm and subtracting:

$\begin{matrix}{{{\ln\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}}} = {2 \cdot \frac{x_{2}^{2} - x_{1}^{2} + {2 \cdot \left( {x_{1} - x_{2}} \right) \cdot x}}{\omega_{0}^{2}}}}{x = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \omega_{0}^{2}}} + x_{1}^{2} - x_{2}^{2}} \right\rbrack}{2 \cdot \left( {x_{1} - x_{2}} \right)}}} & (12)\end{matrix}$

Similarly, the y-axis trajectory can be obtained by

$\begin{matrix}{y = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \omega_{0}^{2}}} + y_{1}^{2} - y_{2}^{2}} \right\rbrack}{2 \cdot \left( {y_{1} - y_{2}} \right)}} & (13)\end{matrix}$

3) Error Solving:

As shown in FIG. 5, the received light intensity values Px1, Px2, Py1,Py2 at the nutation trajectory R_(X1), R_(X2), R_(Y1), R_(Y2) can berecorded by;

$\begin{matrix}{{\ln\frac{P_{{outx}_{1}}}{P_{{inx}_{1}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx}_{1} - {\Delta x}} \right)^{2} + \left( {{Ry} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (14) \\{{\ln\frac{P_{{outx}_{2}}}{P_{{inx}_{2}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx}_{2} - {\Delta x}} \right)^{2} + \left( {{Ry} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (15) \\{{\ln\frac{P_{{outy}_{1}}}{P_{{iny}_{1}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx} - {\Delta\; x}} \right)^{2} + \left( {{Ry}_{1} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (16) \\{{\ln\frac{P_{{outy}_{2}}}{P_{{iny}_{2}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx} - {\Delta\; x}} \right)^{2} + \left( {{Ry}_{2} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (17)\end{matrix}$

By equation (14) subtracting equation (15), and equation (16)subtracting equation (17)

$\mspace{20mu}{{\ln\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}}} = {2 \cdot \frac{{Rx}_{2}^{2} - {Rx}_{1}^{2} + {{2 \cdot \left( {{Rx}_{1} - {Rx}_{2}} \right) \cdot \Delta}\; x}}{\omega_{0}^{2}}}}$$\mspace{20mu}{{\ln\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}}} = {2 \cdot \frac{{Ry}_{2}^{2} - {Ry}_{1}^{2} + {{2 \cdot \left( {{Ry}_{1} - {Ry}_{2}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}}$${E\left( {{\Delta\; A},{\Delta\; y}} \right)} = {\sum\left\lbrack {{2 \cdot \frac{\begin{matrix}{\left( {{Rx}_{n + N}^{2} - {Rx}_{n}^{2}} \right) + {{2 \cdot \left( {{Rx}_{n} - {Rx}_{n + N}} \right) \cdot \Delta}\; x} +} \\{\left( {{Ry}_{n + N}^{2} - {Ry}_{n}^{2}} \right) + {{2 \cdot \left( {{Ry}_{n} - {Ry}_{n + N}} \right) \cdot \Delta}\; y}}\end{matrix}}{\omega_{0}^{2}}} - {\ln\frac{P_{{out}{(n)}}}{P_{{out}{({n + N})}}}}} \right\rbrack}$$\mspace{20mu}{{\Delta\; x} = {\ln{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Rx}_{1}}}}}$$\mspace{20mu}{{\Delta\; y} = {\ln{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Ry}_{1}}}}}$

As mentioned above, a device and method of efficiently coupling spatiallight to optical fiber light without a position detector for obtaining astable optical axis provided by the present invention has the followingbeneficial effects:

(1) The present invention realizes the high-efficiency coupling spatiallight to optical fiber light with a stable optical axis under thecircumstance that there is no position detector;

(2) The present invention can independently calculate the coupling modelparameters without external provision;

(3) The present invention has a simple structure with stable andreliable performance, which can be easy integrated;

(4) the present invention can obtain high coupling efficiency, has astrong ability to filter out background light, can further improve theanti-interference ability, and can realize a relatively excellentspatial light communication transmission channel.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic diagram of steps of a method of efficientlycoupling spatial light to optical fiber light without a positiondetector for obtaining a stable optical axis proposed by the presentinvention.

FIG. 2 shows a schematic diagram of a device of efficiently couplingspatial light to optical fiber light without a position detector forobtaining a stable optical axis proposed by the present invention.

FIG. 3 shows a schematic diagram of the connection structure between anoptical fiber coupler and a coupling lens used in the present invention.A chassis of the optical fiber coupler and a converging lens group arefixed in one lens barrel, so that the end face of the fiber is locatedat the focal point of a lens group.

FIG. 4 shows a schematic structural diagram of an optical fiber couplerused in the present invention. The optical fiber is packed into aceramic tube with the construction of a capillary with a ferrule. A lowend of the ceramic tube is fixed to the chassis to form a cantileverstructure. There are four electrode regions around the ceramic tube.Four electric wires are extended from the electrode regions near a base,and the electric wires re connected to an external signal drive controlboard through the base.

FIG. 5 shows an optical fiber coupling model.

The reference numbers in the figures are as follows:

laser (01), beam collimator (02), two-dimensional fast scanninggalvanometer (03), converging lens group (04), optical fiber coupler(05), drive signal control board (06), signal transmitting module (07),bridge (08), detector (09), data acquisition board (10), optical fibercoupler (11), converging lens group (12), lens barrel (13), lens barrelsupport (14), piezoelectric ceramic tube (15), coupling base (16),electric wire (17), optical fiber (18).

DETAILED DESCRIPTION

The following specific examples are used to illustrate theimplementation of the present invention. Those skilled in the art caneasily understand other advantages and effects of the present inventionfrom the content disclosed in this specification.

It should be noted that the structure, proportion, size, etc. shown inthe accompanying drawings in this specification are only used for theunderstanding and reading of those skilled in the art combining thecontent disclosed in the specification, and are not intended to limitthe conditions under which the present invention can be implemented, soit has no technical significance. Any structural modification,proportional relationship change or size adjustment should still fallwithin the scope of the technical content disclosed in the presentinvention, without affecting the effects and objectives that the presentinvention can produce. At the same time, terms such as “upper”, “lower”,“left”, “right”, “middle” and “a” quoted in this specification are onlyfor the convenience of description and are not intended to limit thescope of the present invention, and the change or adjustment of itsrelative relationship shall be regarded as the scope of theimplementation of the present invention without substantial change ofthe technical content. In the following, the method of efficientlycoupling spatial light to optical fiber light without a positiondetector for obtaining a stable optical axis in the present inventionwill be further described with reference to the accompanying drawings,but the protection scope of the present invention should not be limitedby this.

Embodiment 1

The present invention provides a method of efficiently coupling spatiallight to optical fiber light without a position detector for obtaining astable optical axis, and the specific steps are shown in FIG. 1. Themethod comprises the following four steps:

Step S001: obtaining coupling model parameters.

The laser (01) emits laser light of 1550 nm into the beam collimator(02) through the optical fiber. The emergent light of the beamcollimator (02) is incident on the two-dimensional fast scanninggalvanometer (03) at an angle of 45 degrees. The light beam reflected bythe two-dimensional fast scanning galvanometer (03) is incident on theconverging lens group (04) in parallel. The focal point of an emergentlight beam of the converging lens group (04) is incident on an end ofthe optical fiber coupler (05). Under the circumstance of the opticalfiber coupler (05) without additional signals, when the two-dimensionalfast scanning galvanometer (03) keeps still in the y-direction, itperforms a triangular wave scan with an amplitude of 300 mv and afrequency of 2 Hz in the x-direction, then optical power signal of theoptical fiber coupler (03) is collected with data length of10{circumflex over ( )}6. In the same way, when the two-dimensional fastscanning galvanometer (03) keeps still in the x-direction, it performs atriangle wave scan with amplitude of 300 mv and a frequency of 2 Hz inthe y-direction, and then the optical power signal of the optical fibercoupler (05) is collected. The sine signal of the two-dimensional fastscanning galvanometer (03) would correspond to the position coordinateof the light spot. The position signal of the two-dimensional fastscanning galvanometer (03) corresponding to each point of the opticalpower signals collected twice are substituted into equation (1) andequation (2):

$\begin{matrix}{{\ln\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}}} = {2 \cdot \frac{y_{22}^{2} - y_{11}^{2} + {{2 \cdot \left( {y_{11} - y_{22}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}} & (1) \\{{\ln\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}}} = {2 \cdot \frac{y_{44}^{2} - y_{33}^{2} + {{2 \cdot \left( {y_{33} - y_{44}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}} & (2)\end{matrix}$

Then, equation (3) is obtained

$\begin{matrix}{{{\Delta\; y} = \frac{{\ln{\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}} \cdot \left( {y_{44}^{2} - y_{33}^{2}} \right)}} - {\ln{\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}} \cdot \left( {y_{22}^{2} - y_{11}^{2}} \right)}}}{{\ln{\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}} \cdot 2}\left( {y_{11} - y_{22}} \right)} - {\ln\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}}{2 \cdot \left( {y_{33} - y_{44}} \right)}}}}{{Due}\mspace{14mu}{to}}} & (3) \\{\omega_{0}^{2} = {2 \cdot \frac{y_{22}^{2} - y_{11}^{2} + {{2 \cdot \left( {y_{11} - y_{22}} \right) \cdot \Delta}\; y}}{\ln\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}}}}} & (4)\end{matrix}$

The coupling model parameter ω₀ can be obtained by substituting equation(3) into equation (4).

Step S000: calibrating a time delay of the two-dimensional fast scanninggalvanometer;

Due to the time delay of the two-dimensional fast scanning galvanometer(03) itself, it is necessary to calibrate the delay of thetwo-dimensional fast scanning galvanometer before calculating theposition error.

Sine signals in the X-direction and Y-direction of the fast steeringmirror are respectively loaded.

K=sin(θ1)

Under the circumstance that the optical fiber nutator is not nutating,the optical fiber nutator outputs sine optical power due to the scanningof the fast steering mirror:

G=sin(θ2)

By calculating the phase difference between K and G:

Δ=θ1−θ2

A delay time of the fast steering mirror can be obtained.

For example,

-   -   the fast steering mirror is loaded with a sine signal in the        X-direction, whose frequency is 20 Hz, and amplitude is 50 mv.

K=sin(θ1)

Under the circumstance that the optical fiber nutator is not nutating,the optical fiber nutator outputs sine optical power due to the scanningof the fast steering mirror:

G=sin(θ2)

K and G signals are collected through an oscilloscope, with an adoptionrate of 2.5 e{circumflex over ( )}5, K and G signals in the time domainare converted to that in the frequency domain with zero padding, that is

K1=fft(K,10{circumflex over ( )}7)

G1=fft(G,10{circumflex over ( )}7)

Then the maximum frequency of the frequency domain signals K1 and G1 arerespectively calculated, with the angle corresponding to the maximumfrequency is the phase, wherein

K2=angle(K1(max))

G2=angle(G1(max))

The phase difference in the frequency domain is the time difference inthe time domain, so the delay time of the fast steering mirror is

T=K2−G2

Step S002: obtaining the trajectory of coordinate axis;

The laser (01) emits laser light of 1550 nm into the beam collimator(02) through the optical fiber. The emergent light of the beamcollimator (02) is incident on the two-dimensional fast scanninggalvanometer (03) at an angle of 45 degrees. The light beam reflected bythe two-dimensional fast scanning galvanometer (03) is incident on theconverging lens group (04) in parallel. A focal point of an emergentlight beam of the converging lens group (04) is incident on an end ofthe optical fiber coupler (05). The signal transmitting module (07)transmits a quadrature sine signal with signal amplitude of 2.1V and afrequency of 2 kHz. The signal transmitted by the signal transmittingmodule (07) is transferred to the drive signal control board (06)through coaxial cables. The drive signal control board (06) divides thesignals into four sine signals, in which each two sine signals areorthogonal, and amplifies the voltage to 100V at the same time, and thenloads the signal onto the optical fiber coupler (05) via electric wires,and the optical fiber coupler (05) is nutated under the action of theamplified orthogonal sine signals. The two-dimensional fast scanninggalvanometer (03) is deflected+10 mv and −10 mv in the x-direction undera constant voltage, so as to collect the output coupling optical powerat two positions respectively, that is, the output optical power valuesunder two states are recorded when the incident light spot is positionedat two independent positions (x₁, y0) and (x₂, y0) on the x-axis, andthen are substituted into equations (5) and (6)

$\begin{matrix}{P_{{outx}_{1}} = {P_{in} \cdot B \cdot e^{{- 2} \cdot \frac{{({x - x_{1}})}^{2} + {({y - y_{0}})}^{2}}{\omega_{0}^{2}}}}} & (5) \\{P_{{outx}_{2}} = {P_{in} \cdot B \cdot e^{{- 2} \cdot \frac{{({x - x_{1}})}^{2} + {({y - y_{0}})}^{2}}{\omega_{0}^{2}}}}} & (6)\end{matrix}$

Taking the logarithm and subtracting:

${\ln\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}}} = {2 \cdot \frac{x_{2}^{2} - x_{1}^{2} + {2 \cdot \left( {x_{1} - x_{2}} \right) \cdot x}}{\omega_{0}^{2}}}$

The x-axis trajectory can be obtained

$\begin{matrix}{x = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \omega_{0}^{2}}} + x_{1}^{2} - x_{2}^{2}} \right\rbrack}{2 \cdot \left( {x_{1} - x_{2}} \right)}} & (7)\end{matrix}$

Similarly, the y-axis trajectory can also be obtained

$\begin{matrix}{y = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \omega_{0}^{2}}} + y_{1}^{2} - y_{2}^{2}} \right\rbrack}{2 \cdot \left( {y_{1} - y_{2}} \right)}} & (8)\end{matrix}$

Step S003: Obtaining the position error;

The laser (01) emits laser light of 1550 nm into the beam collimator(02) through the optical fiber. The emergent light of the beamcollimator (02) is incident on the two-dimensional fast scanninggalvanometer (03) at an angle of 45 degrees. The light beam reflected bythe two-dimensional fast scanning galvanometer (03) is incident on theconverging lens group (04) in parallel. A focal point of an emergentlight beam of the converging lens group (04) is incident on an end ofthe optical fiber coupler (05). The signal transmitting module (07)transmits two orthogonal sine signals with signal amplitude of 2.1V anda frequency of 2 kHz. A signal transmitted by the signal transmittingmodule (07) is transferred to the drive signal control board (06)through coaxial cables. The drive signal control board (06) divides thetwo signals into four sine signals which are orthogonal for each groupof two sine signals and amplifies the voltage to 100V at the same time,and then loads the signal onto the optical fiber coupler (05) viaelectric wires, and the optical fiber coupler (05) nutates under actionof the amplified orthogonal sine signals. The output optical powercoupled by the optical fiber coupler (05) enters the bridge (08) via theoptical fiber. An optical signal of the bridge (08) enters the detector(09) via the optical fiber. An electrical signal of the detector (09)enters the data acquisition board (10) via coaxial wires.

When the nutation frequency is 2 kHz, the nutation period is 500 us, andone collected optical power signal is taken every 125 us, that is, thereceived light intensity values Px1, Px2, Py1, Py2 at the nutationtrajectory R_(X1), R_(X2), R_(Y1), R_(Y2) are recorded;

which can be obtained by the optical fiber coupling model, as shown inFIG. 5

$\begin{matrix}{{\ln\frac{P_{{outx}_{1}}}{P_{{inx}_{1}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx}_{1} - {\Delta x}} \right)^{2} + \left( {{Ry} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (14) \\{{\ln\frac{P_{{outx}_{2}}}{P_{{inx}_{2}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx}_{2} - {\Delta x}} \right)^{2} + \left( {{Ry} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (15) \\{{\ln\frac{P_{{outy}_{1}}}{P_{{iny}_{1}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx} - {\Delta\; x}} \right)^{2} + \left( {{Ry}_{1} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (16) \\{{\ln\frac{P_{{outy}_{2}}}{P_{{iny}_{2}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx} - {\Delta\; x}} \right)^{2} + \left( {{Ry}_{2} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (17)\end{matrix}$

Equation (14) subtracts equation (15), and equation (16) subtractsequation (17)

$\mspace{20mu}{{\ln\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}}} = {2 \cdot \frac{{Rx}_{2}^{2} - {Rx}_{1}^{2} + {{2 \cdot \left( {{Rx}_{1} - {Rx}_{2}} \right) \cdot \Delta}\; x}}{\omega_{0}^{2}}}}$$\mspace{20mu}{{\ln\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}}} = {2 \cdot \frac{{Ry}_{2}^{2} - {Ry}_{1}^{2} + {{2 \cdot \left( {{Ry}_{1} - {Ry}_{2}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}}$${E\left( {{\Delta\; A},{\Delta\; y}} \right)} = {\sum\left\lbrack {{2 \cdot \frac{\begin{matrix}{\left( {{Rx}_{n + N}^{2} - {Rx}_{n}^{2}} \right) + {{2 \cdot \left( {{Rx}_{n} - {Rx}_{n + N}} \right) \cdot \Delta}\; x} +} \\{\left( {{Ry}_{n + N}^{2} - {Ry}_{n}^{2}} \right) + {{2 \cdot \left( {{Ry}_{n} - {Ry}_{n + N}} \right) \cdot \Delta}\; y}}\end{matrix}}{\omega_{0}^{2}}} - {\ln\frac{P_{{out}{(n)}}}{P_{{out}{({n + N})}}}}} \right\rbrack}$$\mspace{20mu}{{\Delta\; x} = {\ln{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Rx}_{1}}}}}$$\mspace{20mu}{{\Delta\; y} = {\ln{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Ry}_{1}}}}}$

That is, the light spot position is

W=√{square root over (Δx ² +Δy ²)}

The position of the fast steering mirror is the actual position of thefast steering mirror at this time, which can be set as (k_(g), k_(y))

W _(k)=√{square root over (k _(x) ² +k _(y) ²)}

Finally, the position error is

Δ=W(t0)−W _(k)(t0+T)

Due to fiber nutation, there are −R_(X1)=R_(X2), −R_(Y1)=R_(Y2), so inpractical applications, Δx, Δy can be either positive or negative.

Step S004: adjusting the optical path according to the position error,so that the light spot is at the position with the maximum couplingefficiency;

Since in step S001 ω₀ has been fitted and calculated, this value is onlyrelated to the optical system and fiber mode field distribution,irrespective of anything else, and in principle, this value will notchange. Rx₁, Ry₁ are respectively the nutation radius of the fibernutation in the x-direction and y-direction, which can be obtained fromthe nutation trajectory of step S002, so the position error Δx, Δysignals can be obtained through step S003. The position error signalsare fed back to the two-dimensional fast scanning galvanometer (03)through the coaxial cable. The two-dimensional fast scanninggalvanometer (03) compensates the corresponding error in time, so thatthe light spot is always fixed at the center of the fiber nutation,which cause system has a stable optical axis.

The invention has the advantage of stable and reliable performance, highcoupling efficiency, strong ability to filter out background light, andfurther improved the anti-interference ability, which can realize arelatively excellent spatial optical communication transmission channel.

Embodiment 2

The present invention provides a device of efficiently coupling spatiallight to optical fiber light without a position detector for obtaining astable optical axis. As shown in FIG. 2, the device comprises thefollowing components:

The present invention also provides a device of efficiently couplingspatial light to optical fiber light without a position detector forobtaining a stable optical axis, comprising a laser (01), a beamcollimator (02), a two-dimensional fast scanning mirror (03), aconverging lens group (04), an optical fiber coupler (05), a drivesignal control board (06), a signal transmitting module (07), a bridge(08), a detector (09), and a data acquisition board (10).

Specifically, the optical path connection among respective parts is thatthe laser (01) is connected to a port of the beam collimator (02)through an optical fiber. The emergent light of the beam collimator (02)is incident on the two-dimensional fast scanning galvanometer (03) at anangle of 45 degrees. The light beam reflected by the two-dimensionalfast scanning galvanometer (03) converges to an optical center of theconverging lens group in parallel and is incident into the converginglens group (04). A focal point of an emergent light beam of theconverging lens group (04) is incident on an end of the optical fibercoupler (05). A signal transmitted by the signal transmitting module(07) is transferred to the drive signal control board (06) throughcoaxial cables. The drive signal control board (06) loads the signalonto the optical fiber coupler (05) via electric wires. The opticalpower coupled by the optical fiber coupler (05) enters the bridge (08)via the optical fiber. The optical signal of the bridge (08) enters thedetector (09) via the optical fiber, and an electrical signal of thedetector (09) enters the data acquisition board (10) via coaxial wires.

When coupling of spatial light and optical fiber light so as to form astable optical axis with the use of present invention, firstly, thelaser (01) emits laser light of 1550 nm into the beam collimator (02)through the optical fiber. The emergent light of the beam collimator(02) is incident on the two-dimensional fast scanning galvanometer (03)at an angle of 45 degrees. The light beam reflected by thetwo-dimensional fast scanning galvanometer (03) is incident on theconverging lens group (04) in parallel. A focal point of an emergentlight beam of the converging lens group (04) is incident on an end ofthe optical fiber coupler (05). Under the circumstance of the opticalfiber coupler (05) without additional signals, when the two-dimensionalfast scanning galvanometer (03) keeps still in the y-direction, itperforms a triangular wave scan with an amplitude of 300 mv and afrequency of 2 Hz in the x-direction, then the optical power signal ofthe optical fiber coupler (03) is collected with data length of10{circumflex over ( )}6. In the same way, when the two-dimensional fastscanning galvanometer (03) keeps still in the x-direction, it performs atriangle wave scan with an amplitude of 300 mv and a frequency of 2 Hzin the y direction, and then the optical power signal of the opticalfiber coupler (05) is collected. The sine signal of the two-dimensionalfast scanning galvanometer (03) would correspond to the positioncoordinate of the light spot. The position signal of the two-dimensionalfast scanning galvanometer (03) corresponding to each point of theoptical power signals collected twice are substituted into equation (1)and equation (2):

$\begin{matrix}{{\ln\frac{P_{{outy}_{\;_{11}}}}{P_{{outy}_{22}}}} = {2 \cdot \frac{y_{22}^{2} - y_{11}^{2} + {{2 \cdot \left( {y_{11} - y_{22}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}} & (1) \\{{\ln\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}}} = {2 \cdot \frac{y_{44}^{2} - y_{33}^{2} + {{2 \cdot \left( {y_{33} - y_{44}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}} & (2)\end{matrix}$

Then, equation (3) is obtained

$\begin{matrix}{{{\Delta\; y} = \frac{{\ln{\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}} \cdot \left( {y_{44}^{2} - y_{33}^{2}} \right)}} - {\ln{\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}} \cdot \left( {y_{22}^{2} - y_{11}^{2}} \right)}}}{{\ln{\frac{P_{{outy}_{33}}}{P_{{outy}_{44}}} \cdot 2}\left( {y_{11} - y_{22}} \right)} - {\ln\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}}{2 \cdot \left( {y_{33} - y_{44}} \right)}}}}{{Due}\mspace{14mu}{to}}} & (3) \\{\omega_{0}^{2} = {2 \cdot \frac{y_{22}^{2} - y_{11}^{2} + {{2 \cdot \left( {y_{11} - y_{22}} \right) \cdot \Delta}\; y}}{\ln\frac{P_{{outy}_{11}}}{P_{{outy}_{22}}}}}} & (4)\end{matrix}$

The coupling model parameter coo can be obtained by substitutingequation (3) into equation (4).

Next, the signal transmitting module (07) transmits a quadrature sinesignal with signal amplitude of 2.1V and a frequency of 2 kHz. Thesignal transmitted by the signal transmitting module (07) is transferredto the drive signal control board (06) through coaxial cables. The drivesignal control board (06) amplifies the voltage to 100V and loads thesignal onto the optical fiber coupler (05) via electric wires, and theoptical fiber coupler (05) performs nutation under action of theamplified quadrature sine signal. The two-dimensional fast scanninggalvanometer (03) is deflected+10 mv and −10 mv in the x-direction undera constant voltage, so as to collect the output coupling optical powerat two positions respectively, that is, the output optical power valuesunder two states are recorded when the incident light spot is positionedat two independent positions (x₁, y0) and (x₂, y0) on the x-axis, andthen are substituted into equations (5) and (6)

$\begin{matrix}{P_{{outx}_{1}} = {P_{in} \cdot B \cdot e^{{- 2} \cdot \frac{{({x - x_{1}})}^{2} + {({y - y_{0}})}^{2}}{\omega_{0}^{2}}}}} & (5) \\{P_{{outx}_{2}} = {P_{in} \cdot B \cdot e^{{- 2} \cdot \frac{{({x - x_{2}})}^{2} + {({y - y_{0}})}^{2}}{\omega_{0}^{2}}}}} & (6)\end{matrix}$

Taking the logarithm and subtracting

${\ln\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}}} = {2 \cdot \frac{x_{2}^{2} - x_{1}^{2} + {2 \cdot \left( {x_{1} - x_{2}} \right) \cdot x}}{\omega_{0}^{2}}}$

The x-axis trajectory can be obtained

$\begin{matrix}{x = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \omega_{0}^{2}}} + x_{1}^{2} - x_{2}^{2}} \right\rbrack}{2 \cdot \left( {x_{1} - x_{2}} \right)}} & (7)\end{matrix}$

Similarly, the y-axis trajectory can also be obtained

$\begin{matrix}{y = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \omega_{0}^{2}}} + y_{1}^{2} - y_{2}^{2}} \right\rbrack}{2 \cdot \left( {y_{1} - y_{2}} \right)}} & (8)\end{matrix}$

Next, the output optical power coupled by the optical fiber coupler (05)enters the bridge (08) via the optical fiber. The optical signal of thebridge (08) enters the detector (09) via the optical fiber, and anelectrical signal of the detector (09) enters the data acquisition board(10) via coaxial wires.

When the nutation frequency is 2 kHz, the nutation period is 500 us, andone collected optical power signal is taken every 125 us, that is, thereceived light intensity values Px1, Px2, Py1, Py2 at the nutationtrajectory R_(X1), R_(X2), R_(Y1), R_(Y2) are recorded;

which can be obtained by the optical fiber coupling model, as shown inFIG. 5

$\begin{matrix}{{\ln\frac{P_{{outx}_{1}}}{P_{{inx}_{1}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx}_{1} - {\Delta x}} \right)^{2} + \left( {{Ry} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (14) \\{{\ln\frac{P_{{outx}_{2}}}{P_{{inx}_{2}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx}_{2} - {\Delta x}} \right)^{2} + \left( {{Ry} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (15) \\{{\ln\frac{P_{{outy}_{1}}}{P_{{iny}_{1}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx} - {\Delta\; x}} \right)^{2} + \left( {{Ry}_{1} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (16) \\{{\ln\frac{P_{{outy}_{2}}}{P_{{iny}_{2}} \cdot B}} = {{- 2} \cdot \frac{\left( {{Rx} - {\Delta\; x}} \right)^{2} + \left( {{Ry}_{2} - {\Delta\; y}} \right)^{2}}{\omega_{0}^{2}}}} & (17)\end{matrix}$

Equation (14) subtracts equation (15), and equation (16) subtractsequation (17)

$\mspace{20mu}{{\ln\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}}} = {2 \cdot \frac{{Rx}_{2}^{2} - {Rx}_{1}^{2} + {{2 \cdot \left( {{Rx}_{1} - {Rx}_{2}} \right) \cdot \Delta}\; x}}{\omega_{0}^{2}}}}$$\mspace{20mu}{{\ln\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}}} = {2 \cdot \frac{{Ry}_{2}^{2} - {Ry}_{1}^{2} + {{2 \cdot \left( {{Ry}_{1} - {Ry}_{2}} \right) \cdot \Delta}\; y}}{\omega_{0}^{2}}}}$${E\left( {{\Delta\; A},{\Delta\; y}} \right)} = {\sum\left\lbrack {{2 \cdot \frac{\begin{matrix}{\left( {{Rx}_{n + N}^{2} - {Rx}_{n}^{2}} \right) + {{2 \cdot \left( {{Rx}_{n} - {Rx}_{n + N}} \right) \cdot \Delta}\; x} +} \\{\left( {{Ry}_{n + N}^{2} - {Ry}_{n}^{2}} \right) + {{2 \cdot \left( {{Ry}_{n} - {Ry}_{n + N}} \right) \cdot \Delta}\; y}}\end{matrix}}{\omega_{0}^{2}}} - {\ln\frac{P_{{out}{(n)}}}{P_{{out}{({n + N})}}}}} \right\rbrack}$$\mspace{20mu}{{\Delta\; x} = {\ln{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Rx}_{1}}}}}$$\mspace{20mu}{{\Delta\; y} = {\ln{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \frac{\omega_{0}^{2}}{8{Ry}_{1}}}}}$

The position error signals are fed back to the two-dimensional fastscanning galvanometer (03) through the coaxial cable. Thetwo-dimensional fast scanning galvanometer (03) compensates thecorresponding error in time, so that the light spot is always fixed atthe center of the fiber nutation, which cause the system has a stableoptical axis.

The invention has the advantage of stable and reliable performance, highcoupling efficiency, strong ability to filter out background light, andfurther improved the anti-interference ability, which can realize arelatively excellent spatial optical communication transmission channel.

Embodiment 3

The present invention also provides an optical fiber coupler, whichcomprises an optical fiber, a piezoelectric ceramic tube, a couplingbase, and an electric wire.

As shown in FIG. 3, the optical fiber is structured as a capillary witha ferrule, and an end of the optical fiber is structured as an end capcoating with high permeability film. The outside of the piezoelectricceramic tube is divided into four strip electrode regions, between whichare insulated. The optical fiber is embedded in the piezoelectricceramic tube, and a bottom end of the piezoelectric ceramic tube isfixed to the coupling base. One end of an electric wire extends fromeach electrode region of the piezoelectric ceramic tube close to thebase portion, and the other end of the electric wire passes through thehole on the base. The whole sites on the base where the electric wirespass through are fixed.

When the optical fiber coupler provided by the present invention isapplied to the device of coupling spatial light to optical fiber lightwithout a position detector for obtaining a stable optical axis providedby the present invention, the electric wire connected to thepiezoelectric ceramic tube is connected to the signal output port of thesignal drive control board, and the signal drive control board outputselectrical signals and loads them on the ceramic tube through theelectric wire. When one external voltage is applied to a certainelectrode area, the ceramic tube contracts in the vertical direction,causing a relatively large tilt on the top of the ceramic tube. At thesame time, the application of voltage will cause the ceramic to expandand contract in the axial direction, so as to achieve the control of thepiezoelectric ceramic tube for nutation movement.

1. A method of coupling spatial light to optical fiber light without aposition detector for obtaining a stable optical axis, which is appliedto a device comprising an optical fiber coupler and a two-dimensionalfast scanning galvanometer, wherein the method comprises at least thefollowing steps: Step S002: the optical fiber coupler is nutated underaction of an amplified orthogonal sine signal, and the two-dimensionalfast scanning galvanometer is deflected to two preset positions inx-direction and y-direction under constant voltage, and an outputcoupling optical power of each position is collected respectively, andx-axis and y-axis trajectories on a nutation circumference are obtainedaccording to the optical power; Step S003: the optical fiber coupler isnutated under the action of the amplified orthogonal sine signal, anoptical power signal is collected every preset nutation period, and aposition error signal is obtained according to the collected opticalpower signal and its corresponding coordinate value; and Step S004: anoptical path is adjusted according to the position error signal, therebyobtaining the stable optical axis.
 2. The method of coupling spatiallight to optical fiber light without a position detector for obtaining astable optical axis of claim 1, wherein before the step S002, it furthercomprises: Step S001: coupling model parameters are obtained; and thestep S001 comprises at least the following steps: S001 a: thetwo-dimensional fast scanning galvanometer keeps still in they-direction, and performs a triangular wave scan in the x-direction,then the optical power signal of the optical fiber coupler is collected;the two-dimensional fast scanning galvanometer keeps still in thex-direction, and performs a triangle wave scan in the y-direction tocollect the optical power signal of the optical fiber coupler; S001 b:substituting the optical power signal collected twice in S001 a and theposition signal of the two-dimensional fast scanning galvanometercorresponding to each signal point into an equation to calculatecoupling model parameters.
 3. The method of coupling spatial light tooptical fiber light without a position detector for obtaining a stableoptical axis of claim 2, wherein after the step S001 and before the stepS002, the method comprises the following steps: S002 a: a signaltransmitting module is controlled to transmit two orthogonal sinesignals; S002 b: a drive signal control board divides an input signalinto four amplified sine signals which are orthogonal for each group oftwo sine signals; S002 c: the drive signal control board loads signalsonto the optical fiber coupler via electric wires, and the optical fibercoupler is nutated under action of the amplified orthogonal sinesignals.
 4. The method of coupling spatial light to optical fiber lightwithout a position detector for obtaining a stable optical axis of claim3, wherein an amplitude of the sine signal emitted by the signaltransmitting module in step S002 a is in a range of 1V-2.5V, and afrequency is in a range of 1 kHz-5 kHz.
 5. The method of couplingspatial light to optical fiber light without a position detector forobtaining a stable optical axis of claim 3, wherein the drive signalcontrol board in step S002 c amplifies a voltage into 100V-200V.
 6. Themethod of coupling spatial light to optical fiber light without aposition detector for obtaining a stable optical axis of claim 1,wherein the step S003 comprises at least one of the following steps:S003 a: a signal transmitting module is controlled to transmit twoorthogonal sine signals; S003 b: a drive signal control board divides aninput signal into four amplified sine signals which are orthogonal foreach group of two sine signals; S003 c: the drive signal control boardloads the signals onto the optical fiber coupler via electric wires, andthe optical fiber coupler is nutated under action of the amplifiedorthogonal sine signals; S003 d: an optical power signal is collectedevery a quarter of nutation period; S003 e: substituting the collectedoptical power signal and its corresponding coordinate value into anequation to obtain a position error signal.
 7. The method of couplingspatial light to optical fiber light without a position detector forobtaining a stable optical axis of claim 1, wherein a calculated x-axistrajectory is:${x = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \omega_{0}^{2}}} + x_{1}^{2} - x_{2}^{2}} \right\rbrack}{2 \cdot \left( {x_{1} - x_{2}} \right)}};$and a y-axis trajectory is:${y = \frac{\left\lbrack {{{\frac{1}{2} \cdot \ln}{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \omega_{0}^{2}}} + y_{1}^{2} - y_{2}^{2}} \right\rbrack}{2 \cdot \left( {y_{1} - y_{2}} \right)}};$wherein, x₁, x₂ are x coordinates of two preset positions in thex-direction, y₁, y₂ are y coordinates of two preset positions in they-direction, ω_(0is) a coupling model parameter, P_(outx1) is an outputoptical power corresponding to the position x₁, P_(outx2) is an outputoptical power corresponding to the position x₂, P_(outy1) is an outputoptical power corresponding to the position y₁, and P_(outy2) is anoutput optical power corresponding to the position y₂.
 8. The method ofcoupling spatial light to optical fiber light without a positiondetector for obtaining a stable optical axis of claim 1, wherein errorpositions are: $\begin{matrix}{{\Delta\; x} = {\ln{\frac{P_{{outx}_{1}}}{P_{{outx}_{2}}} \cdot \frac{\omega_{0}^{2}}{8Rx_{1}}}}} \\{{\Delta\; y} = {\ln{\frac{P_{{outy}_{1}}}{P_{{outy}_{2}}} \cdot \frac{\omega_{0}^{2}}{8Ry_{1}}}}}\end{matrix}$ wherein, Rx₁ is the x coordinate on the x-directiontrajectory, Ry₁ is the coordinate on the y-direction trajectory, ω₀ isthe coupling model parameter, P_(outx1) is an output optical powercorresponding to the position Rx₁, P_(outx2) is an output optical powercorresponding to the position Rx₂, P_(outy1) is an output optical powercorresponding to the position y₁, and P_(outy2) is an output opticalpower corresponding to the position Ry₂.
 9. The method of couplingspatial light to optical fiber light without a position detector forobtaining a stable optical axis of claim 1, wherein, before the stepS003 or the step S002, the method further comprises: Step S000: a timedelay of the two-dimensional fast scanning galvanometer is calibrated;specifically, Step S000 comprises the following steps: Step S000 a: asine signal K=sin(θ₁) in the X and Y directions of a fast steeringmirror is loaded respectively; Step S000 b: when the optical fiber isnot nutating, a sine optical power G=sin(θ₂) output by an optical fibernutator is calculated due to the scanning of a fast steering mirror;Step S000 c: by calculating a phase difference between K and GA=θ ₁−θ₂ a delay time of the fast steering mirror can be obtained.
 10. Adevice of coupling spatial light to optical fiber light without aposition detector for obtaining a stable optical axis, which comprises:a laser (01), a beam collimator (02), a two-dimensional fast scanninggalvanometer (03), a converging lens group (04), an optical fibercoupler (05), a drive signal control board (06), a signal transmittingmodule (07), a bridge (08), a detector (09), and a data acquisitionboard (10); the laser (01) is connected to a port of the beam collimator(02) through an optical fiber, emergent light of the beam collimator(02) is incident on the two-dimensional fast scanning galvanometer (03)at an angle of 45 degrees, a light beam reflected by the two-dimensionalfast scanning galvanometer (03) converges to an optical center of theconverging lens group in parallel and is incident into the converginglens group (04), a focal point of an emergent light beam of theconverging lens group (04) is incident on an end of the optical fibercoupler (05), a signal transmitted by the signal transmitting module(07) is transferred to the drive signal control board (06) throughcoaxial cables, the drive signal control board (06) loads the signalonto the optical fiber coupler (05) via electric wires, the opticalpower coupled by the optical fiber coupler (05) enters the bridge (08)via the optical fiber, an optical signal of the bridge (08) enters thedetector (09) via the optical fiber, and an electrical signal of thedetector (09) enters the data acquisition board (10) via coaxial wires.11. The device of coupling spatial light to optical fiber light withouta position detector for obtaining a stable optical axis of claim 10,wherein the optical fiber coupler (05) comprises an optical fiber (11),and a piezoelectric ceramic tube (12).
 12. The device of couplingspatial light to optical fiber light without a position detector forobtaining a stable optical axis of claim 11, wherein the optical fiber(11) passes through the piezoelectric ceramic tube (12) and is fixed tothe piezoelectric ceramic tube (12).
 13. The device of coupling spatiallight to optical fiber light without a position detector for obtaining astable optical axis of claim 12, wherein the piezoelectric ceramic tube(12) includes four electrode regions (13), and electric wires (14) arewelded on each of the four electrode regions (13).
 14. The device ofcoupling spatial light to optical fiber light without a positiondetector for obtaining a stable optical axis of claim 10, wherein thesignal transmitting module (07) is a signal generator
 15. The device ofcoupling spatial light to optical fiber light without a positiondetector for obtaining a stable optical axis of claim 10, wherein thedrive signal control board (06) is a voltage amplifier.
 16. A device ofcoupling spatial light to optical fiber light without a positiondetector for obtaining a stable optical axis, which is configured toperform a method of coupling spatial light to optical fiber lightwithout a position detector for obtaining a stable optical axisaccording to claim
 1. 17. The device of coupling spatial light tooptical fiber light without a position detector for obtaining a stableoptical axis of claim 10, wherein the optical fiber coupler comprises anoptical fiber, a piezoelectric ceramic tube, a coupling base, and aelectric wire; the optical fiber is structured as a capillary with aferrule; the outside of the piezoelectric ceramic tube is divided intoseveral strip electrode regions which are insulated from each other; thecoupling base has holes; the optical fiber is embedded in thepiezoelectric ceramic tube, a bottom end of the piezoelectric ceramictube is fixed to the coupling base, one electric wire extends from eachelectrode region of the piezoelectric ceramic tube close to the baseportion, and the other end of the electric wire passes through the holeon the base.
 18. The device of coupling spatial light to optical fiberlight without a position detector for obtaining a stable optical axis ofclaim 17, wherein an end face of one end of the optical fiber has an endcap coating with high permeability film.
 19. The device of couplingspatial light to optical fiber light without a position detector forobtaining a stable optical axis of claim 17, wherein the number of thestrip electrode regions is four.